Linear actuating mechanisms, also sometimes designated as linear drive or linear actuators, are available in a plurality of sizes and performance classes and are used for plural applications. One example of such an application is the use of a linear actuating mechanism as a drive member in a heating control system or air-conditioning system, e.g. as linear drive for one valve or plural valves for control by thermostats.
For the use of linear actuating mechanisms, it can often be desirable to know certain operational parameters, such as the position of a shaft member of the linear actuating mechanism, e.g. of a leading screw or a push rod, or the force with which the linear actuating mechanism acts on the element to be operated (e.g. a valve). In rather complex control systems, in particular, such as an electronically controlled heating system or air-conditioning system of a building or the like, in which the linear actuating mechanism acts as a controlling element or the like, a respective acquisition of operational parameters is important for a precise control of the adjustments of the valves, or for correcting the same.
So far, in the case of linear actuating mechanisms used in this way, the detection of the force applied is often effected by means of a micro-switch provided at the linear actuating mechanism. The micro-switch is typically arranged such that it is switched when a predetermined position of the shaft member or push rod, which has been determined as a reference position for the application of a limit force, is reached. Thereby, the operation of the linear actuating mechanism is switched off.
This arrangement can be, however, comparatively inaccurate and error-prone. For instance, a calibration can be difficult or impossible, since the position of the micro-switch is usually fixed during manufacture. Optionally, calibration is often effected by a manual adjustment of a pertinently mounted screw/bolt, which, however, involves laborious manual work. Additionally, it is often not possible with such a construction to adjust forces independently. Also, the system is often susceptible to environmental influences, such as a temperature influence that may lead to an expansion or contraction of the material. Thus, systematic errors may affect the detection of the limit force. Furthermore, the micro-switch is switched mechanically, so that pollutions or the like can lead to disturbances. This can lead to damage of the valves or to an insufficient actuation of the valves by the linear actuating mechanism.